Method for processing resistor glass seal compositions employing organic liquid

ABSTRACT

AN IMPROVED METHOD FOR WET MIXING A GLASS SEAL RESISTOR POWDER HAVING FREE BORIC OXIDE IN THE GLASS PHASE WHEREIN THE EXOTHERMIC REACTION BETWEEN THE WATER AND THE BORIC OXIDE IS MINIMIZED AND CONTROLLED THEREBY PRECLUDING CAKING AND BALLING OF THE RESISTOR POWDER, THIS BEING ACHIEVED BY THE ADDITION OF AN ORGANIC LIQUID SOLVENT SELECTED FROM THE GROUP CONSISTING OF TOLUENE, PENTANE, TRICHLOROETHYLENE, METHANOL, AND ETHANOL, IN THE AMOUNT OF APPROXIMATELY 5-20% BY WEIGHT OF THE RESISTOR POWDER.

United States Patent 3,703,387 METHOD FOR PROCESSING RESISTOR GLASS IIC)OMPOSITIONS EMPLOYING ORGANIC Patrick N. Kesten and Richard A. Webb, Davison, and Raymond E. Bedford, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich. No Drawing. Filed Mar. 3, 1969, Ser. No. 804,010 Int. Cl. C04b 33/26 US. Cl. 10646 5 Claims ABSTRACT OF THE DISCLOSURE An improved method for wet mixing a glass seal resistor powder having free boric oxide in the glass phase wherein the exothermic reaction between the water and the boric oxide is minimized and controlled thereby precluding caking and balling of the resistor powder, this being achieved by the addition of an organic liquid solvent selected from the group consisting of toluene, pentane, trichloroethylene, methanol, and ethanol, in the amount of approximately 5-20% 'by weight of the resistor powder.

This invention relates to an improvement in the processing of glass seal resistor powders such as are used in forming the seal in the centerbore of spark plugs as described in Pat. 2,864,884 granted Dec. 16, 1958 to W. E. Counts et al. and in Pat. 3,235,655 issued Feb. '15, 1966 to W. E. Counts et al. and in pending applications Ser. No. 670,178, filed Sept. 25, 1967, D. E. Achey and Ser. No. 692,485, filed Dec. 21, 1967, J. P. Blum. The glass phase of such barium-'borate type glass seal compositions normally contains a high percentage of free boric oxide. In the processing of such powder mixtures water is added to the mixer in order to obtain a moist, clay-like mass of uniform consistency which is suitable for the formation of granules of the desired size by extrusion through a sievelike member. Such processing has been difficult in the past due to the water-glass reaction producing a sticky powder.

It is a primary object of our invention to provide a method for processing glass seal resistor powder containing free boric oxide whereby the water-glass reaction is minimized and substantially controlled. It is another object of our invention to provide a method for processing glass seal resistor powders containing free boric oxide wherein the resultant granules are hard and both uniform in size and bulk density. These and other objects of our invention are achieved by the addition to the dry resistor powder of an organic liquid solvent and lithium carbonate.

In the processing of resistor glass seal powders it has been common practice to add water to the dry mix powder in order to obtain a clay-like consistency suitable to permit granulating to the desired size by forcing the material through a sieve-like member. Where the glass phase of the powder mixture contains a high percentage of free boric oxide, B 0 it has been found that the exothermic reaction between the water and the B 0 produces a sticky powder which results in balling and caking. Temperatures as high as from about 210 to 240 Fahrenheit have been observed with resultant rapid loss of water and formation of a cement-like cake of material. Also, since the degree of heating between powder batches being processed is not readily subject to control, the caking :and balling produced variations in powder size distribution and bulk density to an extent which was unacceptable from the standpoint of the cost of processing due to excessive quantities of oif-size material.

As a result of extended experimentation and testing we have found that the addition of an organic liquid solvent, which may be vaporized without leaving a carbon deposit,

such as toluene, pentane, trichloroethylene, methanol, and ethanol, in an amount of approximately 5-20% by weight of the dry resistor powder, serves to minimize the waterglass reaction with resultant substantial improvement in the processing characteristics of the powder. We have also found that the addition of lithium carbonate, Li CO in an amount of approximately 0.5 by weight of the dry powder, to the powder prior to Wet mixing also assists in reducing the water-glass reaction problem to eliminate caking, and produces a hard granule. In addition, we have found that the lithium carbonate increases the glass seal density in the centerbore of the spark plug.

By way of exemplifying a preferred embodiment, we have obtained excellent results by our improved method in the processing of the following powder used in resistor type spark plugs and containing a barium-borate glass frit consisting of approximately 25% barium oxide, B210, and boric oxide, B 0

It should be understood that other materials may be used in accordance with our invention, i.e., binders other than bentonite, e.g., animal glue and other clays, magnesium-borate type glass frit, inert fillers other than kyanite such as borolon, zircon, mullite, etc., a carbon source other than Thermax and sucrose such as graphite, acetylene black, dextrose, etc., and a semiconductor material other than zirconium oxide such as the materials disclosed in the above-referenced Pats. 2,864,884 and 3,235,655 and applications S.N. 670,178 and SN. 692,485.

In accordance with the method of our invention, the resistor glass seal powder is dry mixed for a period of approximately twenty minutes after the addition thereto of lithium carbonate in an amount of approximately 0.5% by weight of the dry powder. Thereafter, trichloroethylene is added to the premixed dry resistor powder in an amount of approximately 5% by weight though approximately 58% has been found to be a small but effective range. The wet batch is then mixed for a period of from about 5-10 minutes. Water is then added in an amount of approximately 15% by weight though approximately 10- 16% by Weight of the dry powder has been found to be effective, and the mixing is continued for at least twenty minutes. At this point the batch has assumed a clay-like consistency of substantially homogeneous nature and is granulated by being forced through a 20 mesh screen. The granules are then dried followed by screening through a 20 mesh screen, all resistor powder retained on a mesh screen being retained as suitable for use in forming production resistor seals in spark plugs.

The quantities of trichloroethylene and lithium carbonate set forth in the example result in minimizing the water-glass reaction problem while permitting uniformity in granule size and consistency between batches. Also, the wet mixing time is held to a minimum, sufiicient to enable completion of any water-glass reaction, the time being reduced by approximately 50%. We have found that an excess of trichloroethylene results in a weak granule which does not lend itself to subsequent production handling.

From the foregoing description we have shown the manner in which resistor glass seal powders containing a glass phase having free boric oxide may be readily processed by wet mixing without encountering the difficulties caused by the normal water-glass reaction. The resultant glass seal powder may be readily handled and produces a high density resistor seal when subsequently processed as in the manufacture of a resistor glass seal type spark plug. Our invention is further set forth in the claims which follow:

We claim:

1. An improved method for wet mixing a glass seal resistor powder containing free boric oxide in the glass phase in an amount sufficient to cause reaction with water with attendant caking and balling of the resistor powder comprising the steps of dry mixing said resistor powder to obtain a substantially uniform mixture,

adding an organic liquid solvent which may be vaporized without leaving a carbon deposit and selected from the group consisting of toluene, pentane, trichloroethylene, methanol, and ethanol, in an amount of approximately 20% by weight of said resistor powder,

wet mixing said resistor powder to coat the particles with said solvent,

adding water in an amount of approximately -16% by weight of said resistor powder,

continuing to wet mix said resistor powder to form a mixture of substantially uniform consistency, granulating said wet mixed resistor powder to the desired size,

heating said granules to remove said added liquids,

and screening said dried granules to the desired size,

said organic liquid solvent serving to minimize the exothermic reaction between the water and the boric oxide to preclude caking and balling of the resistor powder and nonuniformity of size and bulk density.

2. A method in accordance with claim 1 wherein an amount of approximately 0.5% by weight of lithium carbonate is added to said resistor powder prior to wet mixing to assist in the control of the water-glass reaction and enable the formation of a high density glass seal.

3. A method in accordance with claim 2 wherein trichloroethylene is added as the organic liquid solvent.

4. A method in accordance with claim 3 wherein trichloroethylene is added in an amount of approximately 5-8% by weight.

5. A method in accordance with claim 4 wherein trichloroethylene is added in an amount of approximately 5% by weight and the resistor powder is of the following composition:

Approx. wt. percent OTHER REFERENCES Singer et .al.: Defiooculants, in Industrial Ceramics, New York (1963), pp. 152-153.

St. Pierre, P.D.S., Slip Casting Non-Clay Ceramics, in Kingery, W. 1)., Ceramic Fabrication Processes, New York (1958), pp. -47.

Kingery, W. D., Ceramic Fabrication Processes, New York (Wiley) 1958, p. 47.

Williams, A. E., Transactions. British Ceramic Society, (1951), The Fabrication of Pure CdO and a Study of Its Hydration, pp. 215-224.

JAMES E. PO'ER, Primary Examiner W. .R. SATTERFIELD, Assistant Examiner US. Cl. X.R. 

